Our Closest Black Holes

 The Cosmic Zoo contains some really strange beasts. Stars that are fifty times larger than our sun with surface temperatures above 100,000 degrees, compared to our sun’s temperature of a measly 10,000 degrees. Tiny stars with less than a tenth the mass of our sun and surface temperatures cooler than lava. Supernovae that can outshine an entire galaxy. Neutron stars, large stars that collapsed down to the size of a small city, so dense that a teaspoonful can weigh millions of tons.

Perhaps the weirdest celestial inhabitants are black holes. These form from the remains of giant stars at least 25 times the mass of our sun. They warp space and time in their vicinity. They can devour entire stars and shoot our death rays of energy that can easily destroy a planet with a direct hit.

Fortunately, there are no black holes close to us. At least that we know of. But you can easily spot the resting place of the closest black holes to us.

Stars are born in star clusters, typically a hundred or more at a time. We can identify a few dozen stars born with our sun four and a half billion years ago. All star clusters form lots of small stars, a moderate number of average stars around the size of our sun, and only a few very large stars. Large stars burn out quickly and, if large enough, form black holes.

Photograph of Hyades star cluster in Taurus with the bright star Aldebaran in the lower left. Credit Maurice Toet

The closest star cluster to us is the Hyades star cluster. It sits in the constellation of Taurus, the Bull. It makes the face of the bull with the bright star Aldebaran marking one of the bull’s eyes. The Hyades cluster is only 150 light years away, practically in our backyard as stellar distances go.

The constellations around the Hyades star cluster. It is visible near the eastern horizon at 11:00 p.m. in October, but high in the sky in early February evenings. Map produced using Night Vision star mapping software.

A research team led by Stefano Torniamenti from the University of Padua in Italy studied the distribution and dynamics of stars in the Hyades star cluster. “Our simulations can only simultaneously match the mass and size of the Hyades if some black holes are present at the center of the cluster today,” Torniamenti said.

That’s not surprising. Astronomer Simon Zwart of the University of Cambridge studies the dynamics of star clusters. Though not involved in the new study, he says “Every open cluster older than some 5 million years and containing over 1,000 stars is expected to host a few black holes.”

Taurus is highest in the sky in late winter and early spring but is visible around 11:30 p.m. in the eastern sky. The black holes themselves are invisible, but you can easily spy their home star cluster. 

Each month, I write an astronomy-related column piece for the Oklahoman newspaper. After it is published there, I post that same column to my blog page.

 This is reprinted with permission from the Oklahoman and www.Oklahoman.com.